Posting a list of apps that take advantage of iPhone 4 specific features: Retina Display, Gyroscope.
Retina Display:
http://appshopper.com/entertainment/sketchbook-mobile
http://appshopper.com/games/cro-mag-rally
http://appshopper.com/games/flight-control
Gyroscope and Retina:
http://appshopper.com/games/real-racing
http://appshopper.com/games/eliminategunrange
Retina Display:
http://appshopper.com/entertainment/sketchbook-mobile
http://appshopper.com/games/cro-mag-rally
http://appshopper.com/games/flight-control
Gyroscope and Retina:
http://appshopper.com/games/real-racing
http://appshopper.com/games/eliminategunrange